shallow foundation

GROUP NO.01Name Roll No.

(1) Raktim Barua 10.01.03.123(2) Farjana Akter 10.01.03.140(3) Fatema Sultana 10.o1.03.159(4) Md.Shahadat Hossain 10.01.03.154(5) Raiyan Fardous Ratul 10.01.03.153(6) Sajjad Hossain 10.01.03.152(7) Mehrana Rashid Noor 10.01.03.162(8) Tuhin 10.01.03.156(9) Bushra Tasnim 09.02.03.002

Foundation:Foundation is the lowest part of a structure which 

provides a base for the super‐structure and transmit the loads (live load, wing load) on the structure including the dead weight of the structure itself  to the soil below.  

Types of Foundation:

Foundation can be broadly classified into two types–1. Deep Foundations 2. Shallow Foundations

Shallow foundations:Foundation is placed immediately lowest part of the super structure, is termed as Shallow foundation.

Why we use shallow foundation?

‐ To distribute the structural loads over a wide horizontal area at a shallow depth below the ground level.

The various types of shallow foundations are : 

(a) Spread footing(b) Combined footing(c) Mat or Raft foundation.(d) Grillage footing(e) Eccentrically loaded footing

Spread footings 

Spread footings  are structural members used to support columns and walls and to transmit and distribute their loads to the soil.

Types of spread footing Wall footings Reinforced concrete 

footings Inverted arch footing Column footings

Wall Footing

Support  walls that may be either bearing or nonbearing walls.

Commonly  required to support direct concentric loads.

Why Wall Footing?

Footings carry relatively light loads on well drained cohesive soil.

A wall footing under concentric load behaves similarly  to a cantilever  beam.

Used in low rise buildings.

Why Wall Footing?

Reinforced concrete footing

Why Reinforced concrete footing?Relatively heavy loading 

than wall footing.

Bearing capacity of the 

soil is low. 

In a reinforced concrete wall footing, the behavior is identical to that of wall footing.

Reinforcing steel is placed in the bottom of the footing in a direction perpendicular to the wall like a reinforced concrete beam or slab.

Why Reinforced concrete footing?

Inverted arch footing

When a wall iscomposed ofisolated piers, itis well tocombine all theirfootings intoone, and to stepthe piers down .

Inverted arch footing

COLUMN FOOTINGS

WHY COLUMN FOOTINGS? 

This is one of the most economical types of footings. 

Used when columns are spaced at relatively long distances.

WHY COLUMN FOOTINGS?  Low bending strength.When bearing capacity of soil is good.                                                                                 Carry heavy loads. Used to support single columns.To distribute the load uniformly.

CHARACTERISTICS OF COLUMN FOOTINGS

Constructed with brick, stone or plane concrete.

Circular, rectangular or square in plan.

PROCEDURE OF COLUMN  FOOTINGSEARTHWORK LEVELING

Support

Brick flat soling

9’X9’ Wooded Frame

3”BRICK FLAT SOLING

Joint of rod

Wires  

BINDINGTHE RODS

Upper rod

Inner rod

6” interval

POSITION OF RODS

PLAN

3”Clear cover

6”Block

CLEAR COVERS&

BLOCKS

Centering with plumb bob

Ring

Centre point of column

CENTERING  THE COLUMN

6” Interval ring

PREPARED COLUMNREINFORCEMENT

Length 17”

Width 9”

LENGTH & WIDTH OF RING

PUTTING THE COLUMN INTO THE FOOTING

Load bearing support

CAVING TENDENCY

LEVELLING THE COLUMN

SUPPORTING THE COLUMN

Vibrating 

PORING CEMENT CONCRETE 

A COMPLETE COLUMN FOOTING

Combined footings

Combined  footingsusually support two columns, or three columns not in a row. 

Combined footings are used when tow columns are so close that single footings cannot be used or when one column is located at or near a property line.

When two columns are close together, causing overlap of adjacent isolated footings.When soil bearing capacity is low, causing overlap of adjacent isolated footings.

WHY COMBINED FOOTINGS?

PROCEDURE OF COMBINED FOOTINGS

A COMPLETECOMBINED FOOTING

Foundation which consists of thick reinforced concrete slab covering the entire area of the bottom of the structure like a floor.

This foundation was invented by John Root at Chicago in 19th

century. 

Raft Foundation

Why Raft Foundation?

Base soil has low bearing capacity or the column loads are so large that more than 50% of the area is covered by conventional spread footings.

Resist unequal settlement due to earthquake.

Quickness of the construction work.

Figures of the Different Types of Raft

PROCEDURE OF MAT FOUNDATION

PlanShoringExcavation of soilBrick flat soling                 

or C.C. castingFormwork & 

Placing of reinforcement CastingCuring

Before earth can be excavated to make the foundationcertain precaution has to be taken to stop the outside soilfrom caving in the excavated area. These precautions arecalled shoring , the purpose of which is to anyhow retainthe surrounding soil.

Shoring process

Excavation

Excavate earth according to design

specification

Reinforced chair

Bottom rebar

Top rebar

POSITION OF REBARS

PREPARED COLUMN REINFORCEMENT

SUPPORTING THE COLUMN

Extra top rebar

Position of column on foundation

Support

Column

Formwork for casting

Wooden frame

Support

Pouring cement concrete & compacting 

Spread footers being installed tooshallow, oftentimes just 2‐3 feet belowa foundation, which does not eliminatethe effects of expansive soils.

Foundation repair will last longerthan a week as the excavations aremade and the concrete will have tobe cured before the holes can berefilled.

Limitations of shallow foundation

A huge amount of earthwork is to bedone in Mat foundation.

If the shoring system can not resistthe pressure of outside land, then thestructure surrounding the area may bedamaged by deflection of soil.

Ground water may come out whenthe earthwork is done.

Limited to dealing with point loads.

Limitations of shallow foundation

It is a quick process compared to others inthe construction work.

This type of foundation is alsoeconomically cheaper than any otherfoundations.

Though there are some limitations in matfoundation still it is economical in somecases.

Advantages of shallow foundation

It can resist ground water absorption.

The damage due to earthquake islesser than any other type offoundation.

It consists of a reinforced concrete slab which is more thicker than footing foundation.

It prevents unequal settlements.

Advantages of shallow foundation

We know shallow foundations are not applicable for high rise structures, but we saw a lot of high rise structures which are building upon raft foundation!Generally Raft is used when the bearing capacity of soil is low, but in some sites, we saw raft foundation is used instead of having a good bearing capacity!

Conflicts of Our Knowledgewith Our Experiences

Questions ? ?